been made at it, have never been taken seriously enough to merit the name of theory. With the strictly orthodox, indeed, the cause of gravitation is no longer open to discussion. It has been relegated once for all to the region of the unknowable. A book, therefore, which throughout five hundred pages not only proposes to discuss this forbidden problem, but also professes to solve it, will attract attention for its boldness, if for nothing else. One begins to read with large sense of expectation.
The volume is divided into four books, which deal respectively with methods of inquiry; with first principles; with phenomenology, or "the interconvertibility of forces"; and finally with gravitation. All the books seem to us of value. They have been arranged with considerable cleverness, for the effect is cumulative.
The first book is largely psychological. Its main content has to do with methods of inquiry and of verification, and with sources of error. It maintains, and we think very properly, that our greatest need at the present time is a revision of our conceptions rather than any further confirmation of our observational or experimental data. In all cases the causes of phenomena are inferential, and are necessarily colored by our prior conceptions along the same lines of inquiry. Our stock in trade, when we come to philosophize, is simply the report of our own imperfect senses, helped or hindered, as the case may be, by our equally imperfect reasoning. The same facts may come into different minds, but they have far from equivalent values. It is comparatively easy to agree about the facts, but far from easy to agree about their interpretation. The interpretation is necessarily subjective, and is conditioned by many factors outside the phenomena themselves. Remembering this, one will be disposed to agree with the authors that apparent absurdity is not a legitimate refutation of any new and strange theory. It is only the absence of similar conceptions that makes the new view absurd. Nor does the correspondence of any theoretical view with prior conceptions offer the least confirmation of the view itself. Its agreement with preconceived ideas may prevent its seeming absurd, but does not prevent its being untrue. The so-called "confirmations" of philosophy and science will always bear re-examination, indeed demand such periodical re-examination, and the more so in proportion to their seeming certainty. The shores of the ocean of truth are thickly strewn with the wrecks of many a fair theory, as beloved in its day as the most cherished beliefs of our own day. Equally true is it that agreement between phenomena and theory, however perfect it may be, is not confirmation, for it is to be remembered that the theory itself was deduced from these very phenomena. The argument that such agreement constitutes proof
